We present the results of biochemical and electron microscopic (EM) examinations of the spinal cord myelin from SOD1G93A transgenic Sprague Dawley rats in the early and late symptom-free period of the disease (60 and 93 days of life) and after four-leg paralysis has occurred (120 days of life). Biochemical and ultrastructural changes of myelin started already in the symptom-free period and become most pronounced in the paralyzed animals. Biochemical examinations indicated a decrease of lipids, phospholipids, cholesterol and cerebrosides. The pattern of particular phospholipids was in the normal range. A progressive decrease of the percentages of proteolipid, DM-20
and Wolfgram proteins was evident. Myelin basic proteins I and II were less affected. In EM, massive myelin disorganization was observed.